Promoting and Protecting the City's Health

Rocky Mountain Spotted Fever

(Tick-borne Typhus Fever)

What is Rocky Mountain spotted fever?

Rocky Mountain spotted fever (RMSF) is the most severe tick-borne rickettsial illness in the United States. There are 250 to 1200 cases reported annually in the US. It is a zoonotic disease caused by the bacterium Rickettsia ricketsii . Most cases of RMSF occur in the southeastern and south central United States. RMSF is transmitted to humans and other animals by the bite of an infected tick. Ticks can become infected by feeding on infected animal hosts. However, once infected, an adult tick can pass the infection to its offspring. In the United States, east of the Rocky Mountains and along the Pacific coast, the primary vector is the American dog tick, Dermacentor variabilis . In the Rocky Mountain region, the Rocky Mountain wood tick, Dermacentor andersoni , is the primary vector species. Other ticks, particularly the lone star tick, Amblyomma americanum , may occasionally transmit RMSF. Person-to-person spread of RMSF does not occur. It usually takes several hours of attachment before an infected tick can transmit RMSF bacteria.

Rocky Mountain spotted fever in New York City

Nationally, the disease is reportedly most common in children under 10 years of age, but in NYC the majority of patients are middle-aged. The number of cases reported in NYC has ranged from 2 to 27 per year. For more information on the number of NYC residents reported to have RMSF, please visit Epi Query . The American dog tick can be found in all five boroughs of New York City, as well as nearly all parks and woodlands in the eastern United States. In 1996, an outbreak of RMSF occurred in New York City, primarily in the region of Soundview Park in the Bronx. However, cases of RMSF have occurred in all five boroughs. Adult dog ticks will feed on people, and are most active during the spring, summer, and fall. Most cases of RMSF in New York City are reported during April, May, and June. However, since ticks may be active year-round, disease transmission can also occur at any time of the year.